This invention relates to downhole, pneumatically-operated, impact drilling tools and more particularly to devices for controlling the weight applied to the drilling tools during operation.
To obtain optimum penetration rate, it is necessary for the impact drilling tool to be weighted to maintain the drilling bit in the closed working position within the drilling tool. However, if excessive weight is placed upon the tool, excessive wear and breakage of the tool bit generally results.
Most impact rock drilling tool manufacturers recommend that the weight applied to the tool exceed a minimum weight to keep the tool closed when the bit is in the drilling position but not to exceed a maximum weight which results in shortened bit life. Most manufacturers indicate that an optimum total weight on the tool lies between the minimum and maximum and must be determined by experience. However, in reality, it is relatively difficult to control the weight applied to the tool particularly in relatively deep holes and for changing working pressures. As the working pressure varies, the weight applied to the tool should additionally vary so as to not overload the drill bit. Additionally, constant observation by an operator at the drill rig is a very time-consuming and fatiguing operation. Even with the most experienced operator it is very easy to overload the tool particularly in deep holes, resulting in excessive wear at the drill bit.
Attempts have been made to place a known weight of drill pipe on top of the tool to preload the tool with a telescoping fixture interconnecting the preload drill pipe and the drill string so that a constant load is maintained on the tool. However, with such a system the operator must be able to accurately calculate the necessary preload required. Furthermore, such a system does not accommodate itself to varying working pressures that may be experienced particularly in deep hole drilling. Furthermore, such a system does not overcome the varying friction forces between the preload drill pipe and the hole wall.
One of the principal objects of this invention is to provide a downhole weight control device adjacent the tool for applying a proper preload weight on the tool that is automatically varied in proportion to the working pressure.
An additional object of this invention is to provide a downhole weight control device for applying the correct preload to the tool to maintain the drilling tool in the closed working condition without additionally overloading the drill tool causing excessive wear.
A further object of this invention is to provide a downhole weight control device for attaching to a downhole, pneumatically-operated, impact drilling tool for providing a preload on the tool that maintains the tool operating at optimum penetrating rate without causing excessive wear or breakage of the drill bit.
A still further object of this invention is to provide a downhole weight control device for a downhole, pneumatically-operated, impact drilling tool that increases the life of the tool, drilling bit, drill string, drill swivel, drill rotary table and power heads.
An additional object of this invention is to provide a downhole weight control device for a downhole, pneumatically-operated, impact drilling tool that is capable of optimizing the penetration rate of the tool to obtain straighter holes while still at the same time extending the life of the drill bit.
A further object of this invention is to provide a downhole weight control device for an impact drilling tool that applies the correct preload on the tool regardless of the working air pressure.
A still further object of this invention is to provide a weight control device for an impact drilling tool that provides the correct preload to the tool to obtain optimum penetration rate while at the same time preventing transmission of normal vibrations back up the hole through the drill string.
These and other objects and advantages of this invention will become apparent upon reading of the following detailed description of a preferred embodiment.